In the manufacture of potato chips or other loose product, chips are continuously advanced by a series of vibratory feed conveyors from a cooker to the weighing scale of a form and fill machine wherein successive batches of the chips are separated for packaging. The chips are fed from the discharge end of the last conveyor in the series to a scale hopper for product weighing. When the weight of the chips in the hopper is equal to the desired weight, the scale actuates one or more switches (1) to close a door located between the last conveyor in the series and the access opening of the scale hopper and (2) to open a door located at the egress opening of the scale hopper.
An example of a prior art hopper door mechanism is shown in U.S. Pat. No. 2,904,304, issued Sept. 15, 1959, to Zwoyer et al. As shown therein, a solenoid is mounted on the scale hopper itself and is pivotally connected via a suitable lever system to the hopper door. Actuation of the solenoid in one direction opens the door against the influence of a return spring, while de-energization of the solenoid allows the door to close under the influence of the return spring.
The above-described type of scale hopper door mechanism is not as accurate as is desirable for at least two reasons. In the first place, the weight of the solenoid and its accessory linkages becomes part of the tare weight of the hopper, increasing the tare weight percentage of the total weight and thus reducing the accuracy of the measurement of the product weight percentage of the total weight. And, in the second place, since the solenoid is mounted on the hopper and since the weighing operation is intended to be extremely high-speed, the dynamic effect of the movement of the solenoid is still felt on the hopper during the weighing operations, thereby introducing an unpredictably fluctuating factor into the perceived weight.
Attempts have been made to separate the door operator from the scale hopper to alleviate these problems. In doing so, complicated motion transmission systems including slip links, cams, and/or leaf springs have been used, such as shown in U.S. Pat. No. 3,086,564 issued Apr. 23, 1963 to Staff. The prior devices have been generally rough and noisy in operation and lacking in the desired capability of efficient high speed operation. Furthermore, the prior devices depend on internal springs or the like to restore the scale to zero weight position.
There exists a need, therefore, to provide a scale hopper door mechanism in a form and fill packaging machine of the type described wherein the above mentioned deficiencies are overcome.
Accordingly, one object of the present invention is to provide a new and improved scale hopper door mechanism for quietly and rapidly controlling flow of loose product between a scale hopper and the package of a packaging machine.
Another object of the present invention is to provide a new and improved scale hopper door mechanism in which the hopper is disengaged or separated from the cam opener during the time the scale is making weight.
Still another object is to provide a scale hopper opener wherein a scale restoring force is applied automatically as an adjunct to the opening of the hopper door.
Still another object of the invention is to provide a new and improved scale hopper door mechanism in which a substantially reduced percentage of the weight of the mechanism opening and shutting the hopper door is a part of the tare weight of the hopper and the dynamic effects on the perceived weight of the hopper caused by the movements of the mechanism opening and shutting the hopper door are substantially reduced.